Dog Mood Swings and Allergies

Sorry if this is a dumb post, just looking to hear about other allergy dog sufferers experiences. My dog definitely is becoming a lot more miserable when his allergies flare up.

With myself and my husband (all members of the household), he has never been vicious or aggressive in any way. It is rare that he acts aggressive with other people, but it definitely has happened a few times. He seemed very happy on Zenrelia, however is currently off the drug due to vaccines, and therefore has been quite itchy and uncomfortable lately (even after cytopoint).

An Ex. Of what we have witnessed. My nephew often plays fetch the ball with him. When he was over the other day (dog allergies really bad right now), my nephew went to grab his ball for play time as normal, and our dog snapped, growled, showed teeth.

Im hoping this is just due to being uncomfortable. Has anyone else had similar experiences? Have you seen this behavior decrease with reduction in allergy symptoms? Or do you think I should be working with a trainer on this kind of behavior as well?

Thanks for any input. Just feeling a bit nervous and want to reduce any possibility of "bad" experiences for anyone.